PI: W. Mike Henne, Ph.D. Project Summary/Abstract Lysosomes are the terminal organelle for major cellular catabolic pathways including autophagy and endomembrane trafficking, yet remarkably little is understood about how they rid themselves of the cellular debris they generate. Defects in this efflux contribute to nearly fifty genetic diseases collectively known as lysosomal storage diseases (LSDs), and no universal therapies are available for their treatment. Beyond their roles in catabolic metabolism, lysosomes also supply basic metabolites like fatty acids (FAs) to other organelles of the cell, but the mechanisms that govern this inter-organelle trafficking also remain obscure. I recently characterized a family of proteins that potentially enable this inter-organelle lipid flux. All homologs feature a poorly characterized PX-Associated (PXA), which preliminary data from my lab indicates directly binds to FAs. I hypothesize that PXA domains contribute to non-vesicular inter-organelle lipid exchange. Interestingly, I discovered that the yeast PXA domain-containing protein Mdm1 functions as inter-organelle ?tether? closely connecting the lysosome/vacuole to the Endoplasmic Reticulum, the major lipid synthesis organelle. Mdm1's fly homolog?called Snazurus (Snz)?is also implicated in lipid metabolism and aging, and snz-deficient flies exhibit obesity and hyper-extended lifespan. The human homolog Snx14 was recently implicated in pediatric neurological disease, likely caused by a newly recognized LSD. Collectively, I propose that PXA domain-containing proteins are important mediators of inter-organelle lipid flux and metabolism, and may function to promote the movement of metabolites like FAs between cellular organelles. These proteins thus constitute previously unrecognized but important ?hubs? of lipid metabolism and lysosome homeostasis. The research program outlined here will define the functions of PXA domain-containing proteins in lysosome function and lipid metabolism through three broad approaches: high-throughput genetic screening, the reconstitution of inter-organelle tethering, and developing in organismo lipidomics technologies. By implementing these approaches in my new lab, we will establish ourselves on the leading edge of a paradigm-shifting era that will define new pathways and mechanisms of non-vesicular lipid trafficking. These discoveries promise new therapies for LSDs, as well as new therapeutic strategies for chronic metabolic syndromes like diabetes and heart disease.